Measurement of net ecosystem production and ecosystem respiration in a Zoysia japonica grassland, central Japan, by the chamber method

Measuring light, temperature, soil moisture, and growth provides a better understanding of net ecosystem production (NEP), ecosystem respiration ( R eco ), and their response functions. Here, we studied the variations in NEP and R eco in a grassland dominated by a perennial warm‐season C 4 grass, Zoysia japonica . We used the chamber method to measure NEP and R eco from August to September 2007. Biomass and leaf area index (LAI) were also measured to observe their effects on NEP and R eco . Diurnal variations in NEP and R eco were predicted well by light intensity (PPFD) and by soil temperature, respectively. Maximum NEP (NEP max ) values on days of year 221, 233, 247, and 262, were 2.44, 2.55, 3.90, and 4.17 μmol m −2 s −1 , respectively. Throughout the growing period, the apparent quantum yield ( α ) increased with increasing NEP max that ranged from 0.0154 to 0.0515, and NEP responded to the soil temperature changes by 44% and R eco changes by 48%, and R eco responded from 88 to 94% with the soil temperature diurnally. NEP's light response and R eco 's temperature response were affected by soil water content; more than 27% of the variation in NEP and 67% of the variation in R eco could be explained by this parameter. NEP was strongly correlated with biomass and LAI, but R eco was not, because environmental variables affected R eco more strongly than growth parameters. Using the light response of NEP, the temperature response of R eco , and meteorological data, daily NEP and R eco were estimated at 0.67, 0.81, 1.17, and 1.56 g C m −2 , and at 2.88, 2.50, 3.51, and 3.04 g C m −2 , respectively, on days of year 221, 233, 247, and 262. The corresponding daily gross primary production (NEP + R eco ) was 3.5, 3.3, 4.6, and 4.6 g C m −2 .